Projection display unit

ABSTRACT

A projection display unit ( 1 ) includes a projection optical system ( 10 A), a polarization separation device ( 15 ), and a detection optical system ( 10 B). The projection optical system includes an illuminator ( 11 ), a projection lens ( 16 ), and a light valve ( 12 ) that modulates illumination light supplied from the illuminator on the basis of an image signal, and outputs the modulated illumination light toward the projection lens. The polarization separation device ( 15 ) is disposed between the light valve and the projection lens. The polarization separation device separates entering light into a first polarized component and a second polarized component, and outputs the first polarized component and the second polarized component in respective directions that are different from each other. The detection optical system includes an imaging device ( 13 ) and a reduction optical system ( 14 ). The imaging device is disposed in a position that is optically conjugate with a position of the light valve. The reduction optical system is disposed between the imaging device and the polarization separation device. The imaging device receives, via the projection lens and the polarization separation device, light based on detection invisible light. A transmittance adjuster is provided between the polarization separation device and the imaging device. The transmittance adjuster adjusts transmittance of at least part of a bundle of passing light rays derived from the invisible light.

TECHNICAL FIELD

The disclosure relates to a projection display unit having a detectionfunction.

BACKGROUND ART

In recent years, for example, a smartphone or a tablet terminal mayinclude a touch panel, thereby allowing, for example, page-turning,zooming-in, or zooming-out of an image displayed on a screen to beperformed by an intuitive pointing operation. On the other hand, as adisplay unit that performs display by projecting an image onto a screen,a projector (a projection display unit) has been long known. There isproposed a technology to add a detection function such as that of atouch panel to the projector, for example, as disclosed in PTLs 1 and 2.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2007-52218

PTL 2: Japanese Unexamined Patent Application Publication No. 2003-44839

SUMMARY OF INVENTION

In a projector described in PTL 1, image projection by a projectionoptical system and taking-in of detection invisible light by a detectionoptical system are performed with a single projection lens. Further, alight valve that produces an image and an imaging device that receivesthe invisible light are disposed in positions that are opticallyconjugate with each other. Such a unit configuration allows for accurateobject detection without performing a complicated process such ascalibration. An interactive device is achievable with a simpleconfiguration.

However, such a unit configuration in which a light source appliesinvisible light toward a projection surface, for example, may involve anissue that signal intensity based on the applied invisible light isuneven in a light reception surface, leading to degradation of detectionaccuracy.

Accordingly, it is desirable to provide a projection display unit thatis able to increase detection accuracy.

A projection display unit according to one embodiment of the disclosureincludes a projection optical system, a polarization separation device,and a detection optical system. The projection optical system includesan illuminator, a projection lens, and a light valve. The light valvemodulates illumination light supplied from the illuminator on the basisof an image signal, and outputs the modulated illumination light towardthe projection lens. The polarization separation device is disposedbetween the light valve and the projection lens. The polarizationseparation device separates entering light into a first polarizedcomponent and a second polarized component, and outputs the firstpolarized component and the second polarized component in respectivedirections that are different from each other. The detection opticalsystem includes an imaging device and a reduction optical system. Theimaging device is disposed in a position that is optically conjugatewith a position of the light valve. The reduction optical system isdisposed between the imaging device and the polarization separationdevice. The imaging device receives, via the projection lens and thepolarization separation device, light based on detection invisiblelight. A transmittance adjuster is disposed between the polarizationseparation device and the imaging device. The transmittance adjusteradjusts transmittance of at least part of a bundle of passing light raysderived from the invisible light.

In the projection display unit according to the embodiment of thedisclosure, the imaging device is disposed in the position that isoptically conjugate with the position of the light valve, and theimaging device receives, via the projection lens and the polarizationseparation device, the light based on the invisible light, i.e., part ofthe invisible light reflected by an object. The transmittance adjusteris provided between the polarization separation device and the imagingdevice. The transmittance adjuster adjusts the transmittance of at leastpart of the bundle of passing light rays derived from the invisiblelight. This reduces unevenness of signal intensity in a light receptionsurface of the imaging device, which may be attributable to anapplication intensity distribution of the invisible light, for example.

According to the projection display unit of the embodiment of thedisclosure, the imaging device disposed in the position opticallyconjugate with the position of the light valve receives the light basedon the invisible light via the projection lens and the polarizationseparation device, and the transmittance adjuster that adjusts thetransmittance of at least part of the bundle of passing light raysderived from the invisible light is provided between the polarizationseparation device and the imaging device. Accordingly, it is possible toreduce unevenness of signal intensity in the light reception surface ofthe imaging device. As a result, it is possible to improve detectionaccuracy.

It is to be noted that the above description is mere example of thedisclosure. Effects of the disclosure are not limited to the effectsdescribed above, and may be different from the effects described above,or may further include any other effect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates an appearance and a usage state of aprojection display unit according to one embodiment of the disclosure.

FIG. 2 is a block diagram illustrating a functional configuration of theprojection display unit illustrated in FIG. 1.

FIG. 3 is a schematic side view of the state illustrated in FIG. 1.

FIG. 4 illustrates a configuration example of a near-infrared lightsource illustrated in FIG. 1.

FIG. 5A is a perspective view of a first configuration example of acylinder array lens.

FIG. 5B is a perspective view of a second configuration example of thecylinder array lens.

FIG. 6 illustrates a configuration of a key part of the projectiondisplay unit illustrated in FIG. 1.

FIG. 7 schematically illustrates a configuration example of apolarization separation device together with states of entering lightand output light.

FIG. 8A schematically illustrates a concept of taking-in of detectionlight.

FIG. 8B schematically describes a difference in take-in angle betweendetection positions.

FIG. 8C schematically illustrates an example of detection positioncoordinates.

FIG. 9 schematically describes a difference between a reflection pointand a virtual light emission point of the detection light.

FIG. 10A illustrates a configuration of a key part for describing anarrangement of a blocking plate.

FIG. 10B schematically describes a shape of a plane, of the blockingplate, that is perpendicular to an optical axis, etc.

FIG. 11 schematically illustrates a concept of image display and objectdetection of the projection display unit illustrated in FIG. 1.

FIG. 12 schematically describes setting of a threshold value upon objectdetection and signal intensity.

FIG. 13 illustrates a signal intensity distribution according to acomparative example.

FIG. 14 illustrates a distribution of efficiency of reaching the imagingdevice in a case where the blocking plate is used.

FIG. 15 illustrates a signal intensity distribution in the case wherethe blocking plate is used.

FIG. 16 illustrates a configuration of a key part for describing anarrangement of the blocking plate according to Modification 1.

FIG. 17 schematically describes a partially-transmitting mask accordingto Modification 2.

FIG. 18 illustrates a configuration of a key part for describing anarrangement of the partially-transmitting mask illustrated in FIG. 17.

FIG. 19 illustrates a configuration of a key part for describing apartially-transmitting film according to Modification 3.

MODES FOR CARRYING OUT THE INVENTION

Some embodiments of the disclosure are described in detail belowreferring to the accompanying drawings. It is to be noted that thedescription is given in the following order.

1. Embodiment (An example of a projection display unit in which ablocking plate that partially blocks a bundle of passing light rays isdisposed between relay lenses in a reduction optical system)

2. Modification 1 (Another arrangement example of the blocking plate)

3. Modification 2 (An example of a partially-transmitting mask)

4. Modification 3 (An example of a partially-transmitting film)

1. Embodiment [Configuration]

FIG. 1 illustrates an appearance and a usage state of a projectiondisplay unit (a projection display unit 1) according to one embodimentof the disclosure. FIG. 2 illustrates a functional configuration of theprojection display unit 1. The projection display unit 1 may be, forexample, a projector of a type (a so-called ultra-short throw type) thatprojects an image onto the vicinity of its own while being placed on aflat surface such as a top of a table (or while being mounted on, forexample, a wall surface). The projection display unit 1 may also have afunction of actively performing object detection in addition to theimage display function. As illustrated in FIG. 1, a predetermined inputoperation is allowed to be performed by performing an operation in a waysuch as touching a displayed image with a finger (an indicator 71) in aprojection region (a projection region S11) onto which an image isprojected, as will be described in detail later.

Referring to FIG. 2, the projection display unit 1 may include anilluminator 11, a light valve 12, an imaging device 13, a reductionoptical system 14, a polarization separation device 15, a projectionlens 16, and a signal processor 17. Out of the foregoing members, forexample, the illuminator 11, the light valve 12, and the projection lens16 may configure a projection optical system 10A. Further, for example,the imaging device 13 and the reduction optical system 14 may configurea detection optical system 10B. It is to be noted that, for example,driving of the illuminator 11, the light valve 12, the imaging device13, and the signal processor 17 may be controlled by an unillustratedsystem controller at predetermined timings.

The projection display unit 1 may include a casing provided with anear-infrared light source 40. The near-infrared light source 40 may bea laser light source that outputs near-infrared (NIR) light as invisiblelight for detection, and apply the near-infrared light in an in-planedirection of a plane in the vicinity of a projection surface 110. Inother words, the near-infrared light source 40 may provide, in thevicinity of the projection surface 110, a barrier (a detection lightplane 110A) of the near-infrared light so as to cover the projectionregion S11. Referring to FIG. 3, the detection light plane 110A may beprovided in a plane at a predetermined height “h” from the projectionsurface 110. The predetermined height “h” may be different from a heightof an optical axis that passes through the projection lens 16. Further,the detection light plane 110A may be provided to expand in a radialmanner from the near-infrared light source 40 (from a dot-shaped regionor an extremely-small region) so as to cover the projection region S11.

To give an example, the detection light plane 110A may be provided, forexample, with a thickness (a width in a height direction) from 2 mm to 3mm in a position at the height “h” of about several millimeters to aboutseveral tens of millimeters. Further, the detection light plane 110A maycover the projection region S11 in an in-plane direction. In general,the projection surface 110 is flat. Therefore, in the absence of anyblocking object or the indicator 71 such as a finger and a pointer, thedetection light plane 110A is not blocked. In other words, the imagingdevice 13 monitoring the projection surface 110 may not capture theindicator 71. In this state, when, for example, a finger is brought nearthe projection surface 110, or performs an operation such as touchingthe projection surface 110, the near-infrared light of the detectionlight plane 110A may be blocked by the finger, and be thereby reflectedand diffused. The light reflected by the finger may travel in variousdirections. However, part of the reflected light may be taken in by anaperture of the projection lens 16. This entering light may reach theimaging device 13 via the projection lens 16 and the polarizationseparation device 15. At this time, bright spot diffusion points eachoccurring in a dot shape on the projection surface 110 may be focusedonto a position, on the imaging device 13, corresponding to a positionin a plane of the projected image, because the imaging device 13 isdisposed in the position that is optically conjugate with the positionof the light valve 12 that forms an image. This allows for detection ofa position of an object. Moreover, the ultra-short throw type may beadvantageous in visibility of a screen upon performing of an operation.One reason for this is that projection light of the ultra-short throwtype travels the vicinity of the projection surface 110, which is moredifficult to be blocked by part of a body of a person who performs anoperation.

It is to be noted that the near-infrared light source 40 may beprovided, for example, at a lower part of the casing of the projectiondisplay unit 1 as illustrated; however, the near-infrared light source40 may be disposed adjacent to the projection display unit 1 or may notbe disposed adjacent to the projection display unit 1. The near-infraredlight source 40 may be disposed in a position away from the projectiondisplay unit 1 as long as the detection light plane 110A is so providedas to cover the projection region S11. Alternatively, the near-infraredlight source 40 may be disposed inside the casing (an enclosure) of theprojection display unit 1. In the present embodiment, the near-infraredlight source 40 is allowed to be disposed at a height relatively awayfrom the projection surface 110 owing to optical design that will bedescribed later. This makes it easier to bundle the near-infrared lightsource 40 integrally with the projection display unit 1.

The foregoing detection light plane 110A may achieve a mechanism inwhich, when an object (the indicator 71) is brought into contact with orbrought near the projection surface 110, the near-infrared light isreflected (reflected and diffused) by the indicator 71, and part of thereflected light is taken in by the projection display unit 1 as thedetection light.

Referring to FIG. 4, the near-infrared light source 40 may include anear-infrared laser 42, a collimator lens 43, and a cylinder array lens44, for example. Near-infrared light 41 outputted from the cylinderarray lens 44 may provide the detection light plane 110A. Referring toFIG. 5A, the cylinder array lens 44 may include an array of a pluralityof convex cylinder lenses. The cylinder array lens 44 may be so disposedthat a generatrix 44A of each of the cylinder lenses faces a planeperpendicular to the projection surface 110. It is to be noted that,instead of the convex cylinder array lens 44, a cylinder array lens 45including an array of a plurality of concave cylinder lenses asillustrated in FIG. 5B may be used.

The illuminator 11 may output illumination light L1 toward the lightvalve 12 via the polarization separation device 15. The illuminator 11is not specifically limited as long as the illuminator 11 outputsvisible light as the illumination light L1. For example, the illuminator11 may include an unillustrated blue laser, an unillustrated greenlaser, and an unillustrated red laser.

Referring to FIG. 2 and FIGS. 6 to 13, a configuration of a key part ofthe projection display unit 1 is described below.

(Projection Optical System 10A)

The light valve 12 may be a reflective liquid crystal device such asliquid crystal on silicon (LCOS), for example. The light valve 12 maymodulate a first polarized component (for example, an s-polarizedcomponent Ls1 described later) included in the illumination light L1, onthe basis of image data, for example. A polarization state of the lightmodulated by the light valve 12 may be rotated to be converted into asecond polarized component (for example, a p-polarized component Lp1described later). This modulated light is outputted toward theprojection lens 16 via the polarization separation device 15. It is tobe noted that the light valve 12 may allow for black display byreturning entering light (the s-polarized component Ls1) to thepolarization separation device 15 without changing the polarizationstate thereof. A planar shape of an effective region (an effectiveregion A1 described later) of the light valve 12 may be rectangular, forexample.

The projection lens 16 may project, onto the projection surface 110,light (image light L2) having entered from the light valve 12 via thepolarization separation device 15. The projection lens 16 may be anultra-short throw lens with a throw ratio of 0.38 or smaller, forexample. It is to be noted that the throw ratio is expressed by L/H,where L is a distance from the projection lens 16 to the projectionsurface 110, and H is a width of the projection region S11. Referring toFIGS. 2 and 6, the projection lens 16 may receive the detection light(near-infrared light La1) from a direction opposite to a travelingdirection of the modulated light. In the present embodiment, thedetection light may be taken in via the projection lens 16 of theprojection optical system 10A to be guided to the detection opticalsystem 10B as described above.

(Polarization Separation Device 15)

The polarization separation device 15 separates entering light into thefirst polarized component (for example, the s-polarized component) andthe second polarized component (for example, the p-polarized component),and outputs the first polarized component and the second polarizedcomponent in respective directions that are different from each other.The polarization separation device 15 may include a polarizing beamsplitter (PBS), for example. The polarization separation device 15 mayselectively reflect the first polarized component (reflect the firstpolarized component by a polarization separation surface 150) and allowthe second polarized component to selectively pass therethrough (passthrough the polarization separation surface 150). The present embodimentis described referring to an example case in which the polarizing beamsplitter is used as the polarization separation device 15. However, thepolarization separation device 15 is not limited to the polarizing beamsplitter, and may include a wire grid. In this case, the wire grid hasdifferent characteristics from those of the polarizing beam splitter,therefore selectively reflecting the p-polarized component as the firstpolarized component of entering light and allowing the s-polarizedcomponent as the second polarized component to selectively passtherethrough.

Referring to FIG. 6, the polarization separation device 15 may have fouroptical surfaces (a first surface 15A, a second surface 15B, a thirdsurface 15C, and a fourth surface 15D) and the polarization separationsurface 150, for example. The first surface 15A and the third surface15C may face each other in a uniaxial direction (a right-left directionin the diagram), and the second surface 15B and the fourth surface 15Dmay face each other in a uniaxial direction (a top-bottom direction inthe diagram). In such a configuration, the first surface 15A may receivethe illumination light L1, and the second surface 15B may face the lightvalve 12. The third surface 15C may face the detection optical system10B. The fourth surface 15D may face the projection lens 16.

FIG. 7 illustrates a configuration example of the polarizationseparation device 15. As illustrated, the polarization separation device15 may reflect the first polarized component (the s-polarized componentLs1) out of the illumination light L1 having entered the polarizationseparation device 15 from the first surface 15A to output the reflectedlight from the second surface 15B. Meanwhile, the polarizationseparation device 15 may output, from the third surface 15C, the secondpolarized component (the p-polarized component Lp1) out of theillumination light L1. Further, the polarization separation device 15may output, from the fourth surface 15D, the second polarized component(a p-polarized component Lp2) out of light having entered thepolarization separation device 15 from the second surface 15B (the lightmodulated by the light valve 12). This may allow for image projection bythe projection optical system 10A. Meanwhile, the polarizationseparation device 15 may reflect the first polarized component (ans-polarized component Ls3) out of light (the near-infrared light La1)having entered the polarization separation device 15 from the fourthsurface 15D to output the reflected light from the third surface 15C.The s-polarized component Ls3 may be received by the detection opticalsystem 10B, and light based on the foregoing s-polarized component Ls3may be received by the imaging device 13. Thus, an imaging signal DO maybe obtained by the imaging device 13.

(Detection Optical System 10B)

The imaging device 13 is disposed in a position that is opticallyconjugate with a position of the light valve 12. More specifically, whenthe light valve 12 is a reflective liquid crystal device, the imagingdevice 13 may be so disposed that a display surface (a liquid crystalsurface) where an image is produced and an imaging surface of theimaging device 13 are in a relationship optically conjugate with eachother. The imaging device 13 may include a solid-state imaging devicesuch as a complementary metal-oxide semiconductor (CMOS) and a chargecoupled device (CCD). A planar shape of an effective region (aneffective region A2 described later) of the imaging device 13 may berectangular, for example.

Referring to FIG. 6, an example of the detection optical system 10Bincluding the foregoing imaging device 13 may include a visible lightcut filter 17A, a bandpass filter 17B, the reduction optical system 14(relay lens groups 14A and 14B), a polarizer 18, and the imaging device13 that are disposed in order from a conjugate plane 50 side, forexample.

The visible light cut filter 17A may reduce a visible light component ofentering light. Provision of the visible light cut filter 17A may makeit possible to cut a large quantity of the illumination light L1 toenter the imaging device 13 without turning off a light source of theilluminator 11, even if the polarizing beam splitter is used as thepolarization separation device 15. This may allow nearly only thedetection light to enter the imaging device 13, increasing an S/N ratioto improve detection accuracy. It is to be noted that one visible lightcut filter 17A may be provided in this example; however, the number ofthe visible light cut filter is not limited to one, and may be two ormore. Moreover, the visible light cut filter 17A may be disposed in aposition between the conjugate plane 50 and the reduction optical system14 in this example; however, the visible light cut filter 17A may bedisposed in another position, for example, in a position between thereduction optical system 14 and the imaging device 13.

The bandpass filter 17B may allow a specific wavelength (near-infraredlight) to selectively pass therethrough and reduce other wavelengths.

The polarizer 18 may be an optical member that reduces the secondpolarized component included in the illumination light L1. In thisexample, the polarization separation device 15 as described above mayallow the second polarized component (for example, the p-polarizedcomponent) out of the illumination light L1 to pass therethrough,allowing the p-polarized component to enter the detection optical system10B. This may influence an S/N ratio of the imaging signal obtained inthe imaging device 13. Provision of the polarizer 18 as in the presentembodiment may cut the second polarized component (for example, thep-polarized component) included in the illumination light L1, therebyincreasing the S/N ratio. It is to be noted that the position of thepolarizer 18 is not limited to the illustrated position between thereduction optical system 14 and the imaging device 13. The polarizer 18may be disposed in another position, for example, a position between theconjugate plane 50 and the reduction optical system 14.

The reduction optical system 14 may include one or a plurality of relaylens groups (two relay lens groups 14A and 14B, in this example). Eachof the relay lens groups 14A and 14B may have positive power, andinclude at least one lens. A focal length fi of the relay lens group 14Bmay be so set as to be smaller than a focal length fb of the relay lensgroup 14A. For example, on condition that 2fi is equal to fb (2fi=fb),the relay lens group 14A may be disposed in a position away from theconjugate plane 50 of the light valve 12 by the focal length fb, therelay lens group 14B may be disposed in a position away from theforegoing position of the relay lens group 14A by (fb+fi), and theimaging device 13 may be disposed in a position away from the relay lensgroup 14B by the focal length fi. Such an arrangement of the relay lensgroups 14A and 14B may be equivalent to a case where the imaging device13 is disposed on the conjugate plane 50 while achieving a reductionoptical system. In other words, it is possible to further reduce thesize of the imaging device 13 while maintaining a positionalrelationship conjugate with the light valve 12.

Object detection by means of the foregoing reduction optical system 14may be advantageous to cost reduction. The cost of the imaging device 13may be greatly influenced by the size of the imaging device 13. Cost ofconfiguring the projector is weighted heavily toward the light valve 12and the imaging device 13 as semiconductor components. Therefore, a sizereduction in such components may be advantageous in terms of cost.Moreover, object detection by means of the foregoing reduction opticalsystem 14 may be advantageous in increased flexibility of arrangementattributed to extension of a conjugate point by a relay optical system.For example, spacing between components may be provided, allowing for abending optical system by providing a reflective mirror in the spacing.

In the present embodiment, the foregoing configuration includes atransmittance adjuster (for example, a blocking plate 21 describedlater) disposed between the polarization separation device 15 and theimaging device 13. The transmittance adjuster adjusts transmittance ofat least part of a bundle of passing light rays derived from thenear-infrared light. One reason for this is described below.

First, an outline of taking-in of the near-infrared light is described.As schematically illustrated in FIG. 8A, when the indicator 71 such as afinger is brought into contact with the projection surface 110 or isbrought near the projection surface 110, the near-infrared light La ofthe detection light plane 110A provided in the vicinity of theprojection surface 110 may reach the indicator 71 and be reflected anddiffused in various directions. Specifically, the near-infrared light Lamay be diffused in a range that is on the upper side of the projectionsurface 110, is on the forward side of the indicator 71, and correspondsto one-fourth of a solid angle of a whole sphere. Part (thenear-infrared light La1) of the foregoing reflected and diffused light(scattered light) may be collected by the projection lens 16, andthereafter, the collected light may be taken in by an exit pupil E1 ofthe detection optical system 10B.

A detailed description is given below of the near-infrared light La1 tobe taken in by the detection optical system 10B. Referring to FIG. 8B,upon detection of a position of an object on the projection surface 110,a take-in angle of the near-infrared light La1 (an angle θ formed by theprojection surface 110 and the near-infrared light La1 to enter the exitpupil El of the detection optical system 10B) may differ depending onthe detection position. Specifically, the exit pupil E1 may be in aposition in an upper direction as if being looked up from below whenseen from a position P1 that is nearest to the exit pupil E1. Thetake-in angle θ may be therefore the largest in the position P1.Further, the take-in angle θ may gradually decrease in positions P2 andP3 in order, which are farther from the exit pupil E1 in order. Thetake-in angle θ may be the smallest in a position P4 which is farthestfrom the exit pupil E1.

FIG. 8C and the following Tables 1 to 3 describe an example. Table 1describes projection conditions. It is to be noted that the exit pupilE1 may be provided at a height of 100) mm from the projection surface110 such as a screen and a floor. FIG. 8C describes a positioncoordinate (X, Y, Z) of each of the positions P1 to P4 in the projectionregion S11 provided on the foregoing projection conditions. Further,Table 2 describes a distance to the exit pupil E1 together with theposition coordinate (X, Y, Z) of each of the positions P1 to P4.Further, Table 3 describes an angle (the take-in angle θ) formed by theprojection surface 110 and the exit pupil E1 in each of the positions P1to P4. As can be appreciated, the take-in angle θ may vary depending onthe distance from the exit pupil E1. The take-in angle θ is the greatest(θ=33.7°) in the position P1, and is the smallest (θ=10.5°) in theposition P4. Further, the take-in angle θ is 17.6° in the position P2,and is 12.2° in the position P3.

TABLE 1 Projection conditions Projection size  25 inches Aspect ratio16:9 Diagonal size 635 mm Horizontal size 553 mm Vertical size 311 mm

TABLE 2 Distance to exit pupil (mm) Detection position X Y Z Distance P10 150 100 180 P2 277 150 100 330 P3 0 461 100 472 P4 277 461 100 547

TABLE 3 Angle θ(°) formed with exit pupil P1 33.7 P2 17.6 P3 12.2 P410.5

As can be appreciated from above, the distance to the exit pupil E1 andthe take-in angle θ may vary depending on the detection position. Valuesof the foregoing respective parameters themselves may differ dependingon, for example, the size of the projection region S11, or ultra-shortthrow type lens design. However, the relative relationship in magnitudeof the take-in angle θ depending on the detection position describedabove does not vary. This relationship is therefore utilized to identifythe position of the indicator 71.

It is to be noted that a shift (a difference) may be actually presentbetween a reflection position of the near-infrared light La1 and avirtual light emission position seen from a view point of the imagingdevice 13. For reference, FIG. 9 schematically illustrates a state ofreflection near the indicator 71. An upper diagram illustratesreflection in the position P1, and a lower diagram illustratesreflection in the position P4. As illustrated in FIG. 9, thenear-infrared light La of the detection light plane 110 may reach theindicator 71 and be reflected by the indicator 71. However, in fact,from a view point of the exit pupil E1 (the projection lens 16), thenear-infrared light La1 may be seen as if light is emitted from points(virtual light emission points Pb and Pb2) on the projection surface 110that are located farther, by an oblique component of the height “h”,than reflection points (actual application points) Pa1 and Pa2 at whichthe near-infrared light La1 actually reaches the indicator 71. In otherwords, a difference t1 may be present between the reflection point Pa1corresponding to the actual position of the indicator 71 and the virtuallight emission point Pb1. Similarly, a difference t2 may be presentbetween the reflection point Pa2 and the virtual light emission pointPb2. Further, these differences (elongated amounts of the detectionpositions) may each be influenced by the detection position, i.e., thetake-in angle θ. The differences may each be greater as the take-inangle θ is smaller. In this example, the take-in angle θ in the positionP4 may be the smallest. Therefore, the difference t2 of the position P4may have the maximum value. It is to be noted that the take-in angle θin the position P1 may be the greatest, and the difference t1 of theposition P1 may therefore have the minimum value.

As described above, upon the object detection, part of reflection lightfrom a finger (the indicator 71) may be collected by the projection lens16 (taken in by the projection lens 16) to be received by the imagingdevice 13. In other words, reflection light that is not collected by theprojection lens 16 may be present, which does not contribute to theimaging signal. Accordingly, efficiency of taking-in of the reflectionlight (the near-infrared light) to the projection lens 16 (the exitpupil E1) may influence signal intensity obtained in the imaging device13.

(Taking-In Efficiency)

The taking-in efficiency of the near-infrared light is described indetail. The near-infrared light La1 reflected by the indicator 71 may betaken into the exit pupil E1 to enter the detection optical system 10B.A solid angle ω at which the near-infrared light La1 is taken into theexit pupil E1 at that time may be expressed by the following expression(1). Specifically, the solid angle ω may be expressed with a radius ofthe exit pupil E1, a distance to the exit pupil E1 (Table 2), and acosine component of an angle formed thereby. A ratio of the solid angleω to a range of one-fourth of the whole sphere (4π) may correspond tothe taking-in efficiency (CE), which is expressed by the followingexpression (2).

ω=(the radius of the exit pupil E1)·(the cosine component)/(the distanceto the exit pupil E1)²   (1)

CE=ω/(4π/4)   (2)

Table 4 describes a radius of the exit pupil in each of the positions P1to P4. Table 5 describes the taking-in efficiency in each of thepositions P1 to P4. It is to be noted that each numerical value is avalue normalized by a value in the position P3 as 1.

TABLE 4 Exit pupil size (Normalized) P1 0.09 P2 0.84 P3 1 P4 1.39

TABLE 5 Taking-in efficiency (Normalized) P1 0.50 P2 0.71 P3 1 P4 0.89

(Application Intensity Distribution of Near-Infrared Light)

As appreciated from FIG. 1, the detection light plane 110A may beprovided from a dot-shaped region at a lower part of the projector body.For this reason, an in-plane intensity distribution of the near-infraredlight covering the projection region S11 may have a great bias. This maylargely depend on a distance from the emitting point mainly, althoughthis may also depend on a profile of emitted light. As a result,application intensity corresponding to each of the positions P3 and P4which is far from the emitting point may be relatively lower than thatcorresponding to the position P1 which is close to the emitting point.Table 6 describes application intensity (a representative value in theintensity distribution) of each of the positions P1 to P4. Although anapplication method may have an influence to some extent, it may bedifficult to allow the application intensity to be even in therespective positions. When normalized by the position P3 as 1 that isfar from the emitting point and have the lowest intensity, the positionP1 that is the closest to the emitting point has intensity three timesas high as that. Intensity may be also higher in each of the positionsP2 and P4 than in the position P3.

TABLE 6 Application intensity (Normalized) P1 3.21 P2 2.53 P3 1 P4 1.80

The intensity of light that is guided toward the detection opticalsystem 10B from each of the positions P1 to P4 may be the product of theapplication intensity distribution of the near-infrared light (Table 6)and the foregoing taking-in efficiency (Table 5). Accordingly, the lightintensity may differ between the positions P1 to P4. It is to be notedthat, actually, a difference is present between the reflection point andthe virtual light emission point (FIG. 9) as described above. Thisdifference may influence the light intensity, which may not allow forsimple multiplication.

Further, the difference in light intensity between the detectionpositions may influence intensity (brightness) of the imaging signal.Signal intensity may therefore differ between the detection positions.Upon the object detection, a signal may be taken out by binarizationbased on a certain threshold value (a threshold level), for example.However, variations in signal intensity may make it difficult to takeout the signal with high accuracy. It may be therefore desired to reducea difference in light intensity in both qualitative and quantitativemanners.

In the present embodiment, the foregoing transmittance adjuster isprovided in a predetermined position on an optical path in order tosuppress such a difference in light intensity. A case where the blockingplate 21 is used as an example of the transmittance adjuster isdescribed below.

(Blocking Plate 21)

FIG. 10A illustrates a configuration of a key part of the detectionoptical system 10B. As illustrated, the detection optical system 10B mayinclude the reduction optical system 14 (the relay lens groups 14A and14B) between the conjugate plane 50 and the imaging device 13. Theblocking plate 21 may be disposed between two relay lenses adjacent toeach other in the relay lens groups 14A and 14B included in thereduction optical system 14. A position of the blocking plate 21 on theoptical axis is not particularly limited as long as the position of theblocking plate 21 on the optical axis is between the relay lenses. Inthe present example, the blocking plate 21 may be disposed between therelay lens group 14A which is located on the polarization separationdevice 15 side and an aperture stop 20.

FIG. 10B illustrates an example of a layout of the blocking plate 21 ina plane perpendicular to the optical axis (an optical axis Z1). Theblocking plate 21 may block part of the bundle of passing light rays (abundle of passing light rays LZ) derived from the near-infrared light.Specifically, the blocking plate 21 may have, for example, a shape, asize, and a position (a position on the optical axis Z1, and a positionin the plane perpendicular to the optical axis Z1) that are so set thatthe blocking plate 21 selectively blocks the bundle of passing lightrays from a region that is relatively close to the emitting point of thenear-infrared light source 40 (for example, in the position P1 and aregion in the vicinity of the position P1) out of the detectionpositions. For example, the blocking plate 21 may be provided in aposition that is biased in the plane perpendicular to the optical axisZ1 so that the blocking plate 21 blocks the maximum amount of bundle ofpassing light rays from a part equivalent to the position P1 and doesnot block a bundle of passing light rays from a part equivalent to theposition P3. It may be preferable that the provision of the blockingplate 21 cause the intensity distribution, of the bundle of passinglight rays LZ, to be even in the plane perpendicular to the optical axisZ1. A planar shape of the blocking plate 21 (a shape of a planeperpendicular to the optical axis Z1) is not particularly limited. Forexample, the planar shape of the blocking plate 21 may be a rectangularshape as illustrated. However, the planar shape of the blocking plate 21is not limited thereto, and may be one of an elliptical shape, asemi-circular shape, a trapezoidal shape, and a rectangular shape havingrounded corners. This blocking plate 21 may cut off part of the bundleof passing light rays LZ, and thereby adjust a light amount at the imageheight corresponding to each of the detection positions. It is to benoted that it is preferable to attach and fix the blocking plate 21 ontoa chassis in the unit together with the optical members such as otherlenses.

The signal processor 17 may detect, for example, a position of acharacteristic point of the indicator (an object) 71 such as a humanfinger and a pointer, for example, in association with coordinates inthe projection region S11 on the projection surface 110, on the basis ofthe imaging signal from the imaging device 13. Examples of thecharacteristic point may include a shape of a tip of a human finger, acenter of gravity of the finger, and center of gravity of a hand. Forexample, it is possible to extract the coordinate of such acharacteristic point by performing binarization, with the predeterminedthreshold, on the imaging signal D0 obtained from the imaging device 13.

[Workings and Effects]

Referring to FIG. 11, the projection display unit 1 may project, withthe projection lens 16, image information V1 provided on the light valve12 onto the projection surface 110 to enlarge and display the imageinformation V1 as a projected image V2. The projection surface 110 maybe a top of a table, for example. Moreover, the projection display unit1 may also detect a position of an object on the projection surface 110by means of the imaging signal D0 obtained from the imaging device 13.Examples of the position of the object may include a position Pt1 of thecharacteristic point of the indicator (an object) 71 such as a humanfinger and a pointer.

In the present embodiment, the projection lens 16 may be shared by theprojection optical system 10A and the detection optical system 10B, andthe imaging device 13 is disposed in the position optically conjugatewith the position of the light valve 12. This allows for objectdetection that has a detection region (a detectable region) that issubstantially the same as the projection region S11. Moreover, theforegoing optically-conjugate positional relationship makes it possibleto monitor, via the projection lens 16, the position Pt1 of thecharacteristic point of the indicator 71 on the projection surface 110to be overlapped with the projected image V2. Moreover, for example, itis possible to perform a pointing operation on the projected image V2 byperforming image process on a shape of the indicator 71 by the signalprocessor 17 to detect the coordinates of the position Pt1 of thecharacteristic point of the indicator 71. In this case, any coordinateposition in the projection region S11 may correspond to a coordinateposition in the detection region on a one-to-one basis. Accordingly, acoordinate of the detection position Pt2 for the imaging device 13 maycorrespond to a coordinate of the position Pt1 of the characteristicpoint of the indicator 71. In other words, it is possible to detect anobject by associating the position in the projection region S11 and theposition in the detection region with each other without performing acomplicated signal process such as calibration. It is to be noted thatthe number of the indicator 71 may be two or more. For example,coordinates of tips of fingers of both hands may be detectable. By usingthe position of the characteristic point of the indicator 71 detected insuch a manner, it is possible to perform an intuitive operation as if atouch panel is embedded in the projected image V2 of the projector.

A detailed example of the operation of detecting a position of thecharacteristic point is described. In the present embodiment, theposition detection may be performed using binary data of an opticalimage, of reflection light from an object (the near-infrared light La1),that is formed on the light reception surface of the imaging device 13.Upon such position detection, a difference may be present in intensity(luminance) of the signal depending on the foregoing difference indetection position, i.e., depending on the distance from the emittingpoint of the near-infrared light La and the taking-in efficiency, forexample.

FIG. 12 schematically illustrates examples of light intensitydistributions (g1, g2, and g3) for the respective detection positions.As illustrated, a difference may be present in signal intensitydepending on the difference in detection position. The intensitydistribution g1 may be an intensity distribution in a part equivalent tothe position P1, for example. The intensity distribution g3 may be anintensity distribution in a part equivalent to the position P3, forexample. The intensity distribution g2 may be an intensity distributionin a part equivalent to the position P2, for example.

The binarization may involve setting of a predetermined threshold value.The threshold value may be preferably set to a value that allows forextraction of a characteristic point while removing a noise (such as anelectric noise and an unnecessary optical component). For example, in acase where a threshold value Th1 (a constant value) illustrated in FIG.12 is set, a size of the characteristic point may be small in a placehaving low light intensity (the intensity distribution g3). This mayallow for accurate detection of two points (Lp3 a and Lp3 b) that areclose to each other such as two fingers, for example. However, in thecase where the threshold value Th1 is used, two points (Lp2 a and Lp2 bor Lp1 a and Lp1 b) that are close to each other may be continuous witheach other in a place having relatively high light intensity (theintensity distributions g1 and g2). Such two points may be extracted asa single point. This does not contribute to improvement in detectionaccuracy.

It is to be noted that the foregoing issue may be avoidable to someextent by varying the level of the threshold value. For example, in astate that the signal is not saturated as in the intensity distributiong2, it is possible to accurately detect the two points (Lp2 a and Lp2 b)that are close to each other by allowing the threshold value to bevariable in accordance with the intensity distribution. However, thismethod involves difficulty in setting of the optimal threshold value ina state where the signal is saturated as in the intensity distributiong1.

To address this, part of the bundle of passing light rays derived fromthe near-infrared light La1 may be blocked by providing the foregoingblocking plate 21 in the reduction optical system 14 in the presentembodiment. Specifically, by blocking the bundle of passing light raysfrom the position P1 having high light intensity and the vicinity of theposition P1, unevenness of intensity is moderated in the light intensitydistribution on the light reception surface of the imaging device 13.This may reduce the light amount at the part (corresponding to theposition P1) having high light intensity, thereby suppressing saturationof signal. In contrast, the light amount may involve almost no variationat the part (corresponding to the position P3) having low lightintensity. Therefore, the signal may not be buried in the noise. As aresult, setting of the threshold value based on binarization may be madeeasier, allowing for extraction of the characteristic point with highaccuracy. To give an example, saturation may be avoidable when a signalhaving high intensity is set to 256 which is the maximum in 256gradations, and a signal having low intensity is allowed to besuppressed to about 50 which is about one-fifth of the signal havinghigh intensity (when the in-plane luminance ratio is equal to or smallerthan 5).

FIG. 13 illustrates, as a comparison example, a light intensitydistribution on the light reception surface in a case without theblocking plate 21. As illustrated, unevenness of intensity occurs whenthe blocking plate 21 is not used. In contrast, the efficiency ofreaching the light reception surface of the imaging device 13 may be asillustrated in FIG. 14 in the present embodiment, owing to provision ofthe blocking plate 21. As a result, the light intensity distribution onthe light reception surface may be substantially even as illustrated inFIG. 15.

As described above, according to the present embodiment, the imagingdevice 13 disposed in a position that is optically conjugate with theposition of the light valve 12 receives the light based on thenear-infrared light La1 via the projection lens 16 and the polarizationseparation device 15. The blocking plate 21 that blocks part of thebundle of passing light rays derived from the near-infrared light La1may be provided between the polarization separation device 15 and theimaging device 13. The blocking plate 21 may be provided in thereduction optical system 14 in this example. This reduces unevenness(non-uniformity) of signal intensity in the light reception surface ofthe imaging device 13. As a result, it is possible to improve detectionaccuracy.

Some modifications of the foregoing embodiment are described below. Itis to be noted that components similar to those in the foregoingembodiment are denoted with the same numerals and are not furtherdescribed where appropriate.

<Modification 1>

FIG. 16 describes an arrangement configuration of the blocking plate 21according to Modification 1. The blocking plate 21 may be disposedbetween the relay lens group 14A and the aperture stop 20 in thereduction optical system 14 in the foregoing embodiment. However, theblocking plate 21 may be disposed between the aperture stop 20 and therelay lens group 14B as in the present modification. In other words, theblocking plate 21 may be disposed in any position between two relaylenses in the plurality of relay lenses.

It is possible to achieve effects similar to those of the foregoingembodiment also in the present modification by appropriately setting theshape, the position, and the size of the blocking plate 21 as in theforegoing embodiment.

<Modification 2>

FIG. 17 illustrates a configuration of a transmittance adjuster (apartially-transmitting mask 21A) according to Modification 2. Thepartially-transmitting mask 21A may be an optical device havingtransmittance that varies in a segmented manner in a plane perpendicularto the optical axis Z1 of the bundle of passing light rays.Specifically, the transmittance may be relatively lower in a region D1corresponding to a bundle of passing light rays from a part includingthe position P1, and the transmittance may be relatively higher in aregion D3 corresponding to a bundle of passing light rays from a partincluding the position P3. Further, in a region D2 between the regionsD1 and D3, the transmittance may be intermediate between thetransmittance in the region D1 and the transmittance in the region D3.The partially-transmitting mask 21A may preferably have a transmittancedistribution that causes an intensity distribution, in the planeperpendicular to the optical axis Z1 of the bundle of passing lightrays, to be even. In this example, segmentation into the three regionsD1 to D3 may be performed, and the transmittance may be caused to bedifferent between the regions D1 to D3 from each other. However, thenumber of segmentation of the region is not limited to three. The numberof segmentation of the region may be two, or four or more. For example,the areas and the segmentation pattern of the respective regions arealso not limited to those illustrated. Further, the transmittance mayvary in a continuous manner.

The foregoing partially-transmitting mask 21A may be disposed, forexample, in a position (which is denoted with A1) between the surface15C of the polarization separation device 15 and the reduction opticalsystem 14 (the relay lens group 14A), in the key configurationillustrated in FIG. 18. Alternatively, the foregoingpartially-transmitting mask 21A may be disposed in a position (which isdenoted with A2) between the imaging device 13 and the reduction opticalsystem 14 (the relay lens group 14B) in FIG. 18. However, thepartially-transmitting mask 21A may be disposed in the reduction opticalsystem 14, i.e., between two relay lenses adjacent to each other in therelay lens groups 14A and 14B.

As in the present modification, the partially-transmitting mask 21A maybe used as the transmittance adjuster. It is also possible in this caseto reduce unevenness of the signal intensity in the light receptionsurface of the imaging device 13 as in the foregoing embodiment, byadjusting the transmittance of the bundle of passing light rays for eachof the regions. As a result, it is possible to achieve effects similarto those of the foregoing embodiment.

<Modification 3>

FIG. 19 describes a configuration of a transmittance adjuster (apartially-transmitting film 21B) according to Modification 3. Thepartially-transmitting film 21B may be adhered onto the surface 15C ofthe polarization separation device 15. The partially-transmitting film21B may have transmittance that varies in a segmented manner in a planeperpendicular to the optical axis Z1 of the bundle of passing lightrays, as with the foregoing partially-transmitting mask. Thepartially-transmitting film 21B may have a configuration similar to theconfiguration of the foregoing partially-transmitting mask 21A exceptfor that the partially-transmitting film 21B may be provided not as asingle device but as a film and provided integrally with thepolarization separation device 15. Effects equivalent to the effects inthe foregoing embodiment may be achievable also by using the foregoingpartially-transmitting film 21B.

The disclosure is not limited to the description of the foregoingembodiments, and may be modified in a variety of ways. For example, theforegoing embodiment is described referring to an example case where thelight valve 12 and the imaging device 13 have aspect ratiossubstantially the same as each other. However, the light valve 12 andthe imaging device 13 may not necessarily have the same aspect ratio.

Moreover, in the foregoing embodiment, the reflective liquid crystaldevice is used as the light valve of the disclosure. However, the lightvalve of the disclosure is not limited to the reflective liquid crystaldevice and may be another light valve. For example, a digital mirrordevice (DMD) may be used as the light valve. In this case, the lightvalve may be of a mirror type that does not utilize polarizationcharacteristics of light. Therefore, a polarization optical system isnot used in general. However, an optical system including a polarizationseparation device such as a polarizing beam splitter in an optical pathis allowed to be provided as with the foregoing embodiment to achieveimage display using the DMD.

Moreover, the foregoing embodiment is described referring to theultra-short throw type as one example of the projection display unit ofthe disclosure. However, the projection display unit of the disclosureis not necessarily limited thereto. In a case where invisible light hasan application intensity distribution, the application intensitydistribution of the invisible light may cause unevenness of lightintensity on a light reception surface. The configuration of thedisclosure may be therefore effective in such a case. However, theeffects may be especially effective for the ultra-short throw type. Itis to be noted that the effects described in the foregoing embodiment,etc. are mere examples. Any other effect may be provided, and any othereffect may be further included.

For example, the disclosure may achieve the following configurations.

-   [1]

A projection display unit including:

a projection optical system including

-   -   an illuminator,    -   a projection lens, and    -   a light valve that modulates illumination light supplied from        the illuminator on the basis of an image signal, and outputs the        modulated illumination light toward the projection lens;

a polarization separation device disposed between the light valve andthe projection lens, the polarization separation device separatingentering light into a first polarized component and a second polarizedcomponent, and outputting the first polarized component and the secondpolarized component in respective directions that are different fromeach other; and

a detection optical system including an imaging device and a reductionoptical system, the imaging device being disposed in a position that isoptically conjugate with a position of the light valve, and thereduction optical system being disposed between the imaging device andthe polarization separation device, in which

the imaging device receives, via the projection lens and thepolarization separation device, light based on detection invisiblelight, and

a transmittance adjuster is disposed between the polarization separationdevice and the imaging device, the transmittance adjuster adjustingtransmittance of at least part of a bundle of passing light rays derivedfrom the invisible light.

-   [2]

The projection display unit according to [1], in which

the detection optical system includes a plurality of relay lensesserving as the reduction optical system,

the transmittance adjuster is a blocking plate that blocks part of thebundle of passing light rays derived from the invisible light, and

the blocking plate is disposed between any two relay lenses that areadjacent to each other in the plurality of relay lenses in the reductionoptical system.

-   [3]

The projection display unit according to [1] or [2], in which

the transmittance adjuster is a partially-transmitting mask that hastransmittance, of the invisible light, that varies in a segmented manneror in a continuous manner in a plane perpendicular to an optical axis,and

the partially-transmitting mask is disposed between the polarizationseparation device and the reduction optical system.

-   [4]

The projection display unit according to [1] or [2], in which

the transmittance adjuster is a partially-transmitting mask that hastransmittance, of the invisible light, that varies in a segmented manneror in a continuous manner in a plane perpendicular to an optical axis,and

the partially-transmitting mask is disposed between the imaging deviceand the reduction optical system.

-   [5]

The projection display unit according to [1] or [2], in which

the detection optical system includes a plurality of relay lensesserving as the reduction optical system,

the transmittance adjuster is a partially-transmitting mask that hastransmittance, of the invisible light, that varies in a segmented manneror in a continuous manner in a plane perpendicular to an optical axis,and

the partially-transmitting mask is disposed between any two relay lensesthat are adjacent to each other in the plurality of relay lenses in thedetection optical system.

-   [6]

The projection display unit according to [1] or [2], in which thetransmittance adjuster is a partially-transmitting film, thepartially-transmitting film being adhered onto an optical surface, ofthe polarization separation device, that outputs light toward thedetection optical system, and having transmittance, of the invisiblelight, that varies in a segmented manner or in a continuous manner in aplane perpendicular to an optical axis.

-   [7]

The projection display unit according to any one of [1] to [6], in whichan in-plane luminance ratio of an imaging signal obtained from theimaging device is equal to or smaller than 5.

-   [8]

The projection display unit according to any one of [1] to [7], furtherincluding a laser light source that applies the invisible light in aradial manner in an in-plane direction in vicinity of the projectionsurface.

-   [9]

The projection display unit according to any one of [1] to [8], in whichthe invisible light is near-infrared light.

The projection display unit according to any one of [1] to [9], in whichthe transmittance adjuster has a transmittance distribution that causesintensity distribution, of the bundle of passing light rays derived fromthe invisible light, to be even in a plane perpendicular to an opticalaxis.

-   [11]

The projection display unit according to any one of [1] to [10], furtherincluding a signal processor that detects a position of an object on theprojection surface on the basis of an imaging signal obtained from theimaging device.

-   [12]

The projection display unit according to any one of [1] to [11], inwhich the polarization separation device is a polarizing beam splitter.

-   [13]

The projection display unit according to any one of [1] to [12], inwhich the light valve is a reflective liquid crystal display device.

The projection display unit according to [13], in which

the polarization separation device has a first surface, a secondsurface, a third surface, and a fourth surface that each serve as alight entering surface or a light output surface, and

the polarization separation device outputs, from the second surface, thefirst polarized component out of light that has entered the polarizationseparation device from the first surface, outputs, from the thirdsurface, the second polarized component out of the light that hasentered the polarization separation device from the first surface,outputs, from the fourth surface, the second polarized component out oflight that has entered the polarization separation device from thesecond surface, and outputs, from the third surface, the first polarizedcomponent out of light that has entered the polarization separationdevice from the fourth surface.

-   [15]

The projection display unit according to [14], in which

the projection optical system causes

-   -   the illuminator to output the illumination light toward the        first surface of the polarization separation device,    -   the light valve to modulate the first polarized component, out        of the illumination light, that has been outputted from the        second surface of the polarization separation device, and output        light resulting from the modulation toward the second surface of        the polarization separation device, and    -   the projection lens to project, toward the projection surface,        light, out of the light resulting from the modulation, that has        been outputted from the fourth surface of the polarization        separation device.

-   [16]

The projection display unit according to [15], in which the detectionoptical system causes the reduction optical system to receive objectdetection light via the

-   -   projection lens, the fourth surface of the polarization        separation device, and the third surface of the polarization        separation device, and    -   the imaging device to receive light outputted from the reduction        optical system.

This application is based upon and claims the benefit of priority of theJapanese Patent Application No. 2014-172425 filed in the Japan PatentOffice on Aug. 27, 2014, the entire contents of which are incorporatedherein by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A projection display unit comprising: a projection optical systemincluding an illuminator, a projection lens, and a light valve thatmodulates illumination light supplied from the illuminator on a basis ofan image signal, and outputs the modulated illumination light toward theprojection lens; a polarization separation device disposed between thelight valve and the projection lens, the polarization separation deviceseparating entering light into a first polarized component and a secondpolarized component, and outputting the first polarized component andthe second polarized component in respective directions that aredifferent from each other; and a detection optical system including animaging device and a reduction optical system, the imaging device beingdisposed in a position that is optically conjugate with a position ofthe light valve, and the reduction optical system being disposed betweenthe imaging device and the polarization separation device, wherein theimaging device receives, via the projection lens and the polarizationseparation device, light based on detection invisible light, and atransmittance adjuster is disposed between the polarization separationdevice and the imaging device, the transmittance adjuster adjustingtransmittance of at least part of a bundle of passing light rays derivedfrom the invisible light.
 2. The projection display unit according toclaim 1, wherein the detection optical system includes a plurality ofrelay lenses serving as the reduction optical system, the transmittanceadjuster is a blocking plate that blocks part of the bundle of passinglight rays derived from the invisible light, and the blocking plate isdisposed between any two relay lenses that are adjacent to each other inthe plurality of relay lenses in the reduction optical system.
 3. Theprojection display unit according to claim 1, wherein the transmittanceadjuster is a partially-transmitting mask that has transmittance, of theinvisible light, that varies in a segmented manner or in a continuousmanner in a plane perpendicular to an optical axis, and thepartially-transmitting mask is disposed between the polarizationseparation device and the reduction optical system.
 4. The projectiondisplay unit according to claim 1, wherein the transmittance adjuster isa partially-transmitting mask that has transmittance, of the invisiblelight, that varies in a segmented manner or in a continuous manner in aplane perpendicular to an optical axis, and the partially-transmittingmask is disposed between the imaging device and the reduction opticalsystem.
 5. The projection display unit according to claim 1, wherein thedetection optical system includes a plurality of relay lenses serving asthe reduction optical system, the transmittance adjuster is apartially-transmitting mask that has transmittance, of the invisiblelight, that varies in a segmented manner or in a continuous manner in aplane perpendicular to an optical axis, and the partially-transmittingmask is disposed between any two relay lenses that are adjacent to eachother in the plurality of relay lenses in the detection optical system.6. The projection display unit according to claim 1, wherein thetransmittance adjuster is a partially-transmitting film, thepartially-transmitting film being adhered onto an optical surface, ofthe polarization separation device, that outputs light toward thedetection optical system, and having transmittance, of the invisiblelight, that varies in a segmented manner or in a continuous manner in aplane perpendicular to an optical axis.
 7. The projection display unitaccording to claim 1, wherein an in-plane luminance ratio of an imagingsignal obtained from the imaging device is equal to or smaller than 5.8. The projection display unit according to claim 1, further comprisinga laser light source that applies the invisible light in a radial mannerin an in-plane direction in vicinity of the projection surface.
 9. Theprojection display unit according to claim 1, wherein the invisiblelight is near-infrared light.
 10. The projection display unit accordingto claim 1, wherein the transmittance adjuster has a transmittancedistribution that causes intensity distribution, of the bundle ofpassing light rays derived from the invisible light, to be even in aplane perpendicular to an optical axis.
 11. The projection display unitaccording to claim 1, further comprising a signal processor that detectsa position of an object on the projection surface on a basis of animaging signal obtained from the imaging device.
 12. The projectiondisplay unit according to claim 1, wherein the polarization separationdevice is a polarizing beam splitter.
 13. The projection display unitaccording to claim 1, wherein the light valve is a reflective liquidcrystal display device.
 14. The projection display unit according toclaim 13, wherein the polarization separation device has a firstsurface, a second surface, a third surface, and a fourth surface thateach serve as a light entering surface or a light output surface, andthe polarization separation device outputs, from the second surface, thefirst polarized component out of light that has entered the polarizationseparation device from the first surface, outputs, from the thirdsurface, the second polarized component out of the light that hasentered the polarization separation device from the first surface,outputs, from the fourth surface, the second polarized component out oflight that has entered the polarization separation device from thesecond surface, and outputs, from the third surface, the first polarizedcomponent out of light that has entered the polarization separationdevice from the fourth surface.
 15. The projection display unitaccording to claim 14, wherein the projection optical system causes theilluminator to output the illumination light toward the first surface ofthe polarization separation device, the light valve to modulate thefirst polarized component, out of the illumination light, that has beenoutputted from the second surface of the polarization separation device,and output light resulting from the modulation toward the second surfaceof the polarization separation device, and the projection lens toproject, toward the projection surface, light, out of the lightresulting from the modulation, that has been outputted from the fourthsurface of the polarization separation device.
 16. The projectiondisplay unit according to claim 15, wherein the detection optical systemcauses the reduction optical system to receive object detection lightvia the projection lens, the fourth surface of the polarizationseparation device, and the third surface of the polarization separationdevice, and the imaging device to receive light outputted from thereduction optical system.